This got me thinking too, what if other more established places like Trustedplaces, Last.FM, etc also gave away a APML file as part of the profile of each user?

One of the things I loved about APML is the Implicit Data (U-AR) and Explicit Data (I-AM) elements. You can just imagine how simple it would be to output APML from something Last.FM. (whats below isn't true APML markup, just my lazy json like writing)

He also mentions being asked "What is the business imperative to support such a thing".

In other words - if companies make their money from data lockin - then why would they want to give that data away.

I would suggest that anyone asking that question consider that publishers used to think like that. Now they all support RSS.

If feed readers thought like that, then OPML support and the rise of proper and continued innovation in the space may not have occurred.

If you are a smaller guy, supporting APML means that users can jump in and get started quickly. The barrier to entry is lowered.

If you are a bigger player it means an increasingly savvy user base will continue to trust your data mining activities. Also it means you can get a more complete picture of your users if they choose to share their APML from other services. It also means you become part of an ecosystem instead of a data silo - data silos are dead.

In the era of user empowerment, the business imperative is: play nice or users will move to other services that respect their rights. Just watch the mad rush to Facebook.